So many hours of talks , so little progress .

Despite two days of intensive negotiations , Iran and six world powers `` remain far apart '' on Tehran 's controversial nuclear program , EU foreign policy chief Catherine Ashton said Saturday in Kazakhstan .

Her words dashed hopes that the deadlock might be broken after what had seemed more promising talks back in February , also in the Kazakh city of Almaty .

Iran 's top nuclear negotiator , Saeed Jalili , acknowledged there was `` some distance '' between Iran and the six powers but seemed more positive in his assessment .

`` Good negotiations '' had taken place in this round of talks , Jalili said , which he described as `` substantive , expansive and comprehensive . ''

But in a sign that progress was limited , no date or location has been set for new talks .

This round was just the latest in a decade-long attempt to resolve differences between Iran and the international community over Tehran 's nuclear ambitions .

The first day of talks proved inconclusive . By the end of Saturday , despite `` long and intensive discussions , '' the two sides were no closer on agreeing on confidence-building measures , Ashton told reporters .

`` It became clear that the positions of -LRB- the world powers -RRB- and Iran remain far apart on the substance , '' she said .

`` We therefore agreed all sides will go back to their capitals to evaluate where we stand on the process . ''

Ashton said she would be in touch with Jalili `` very soon in order to see how to go forward . ''

While Ashton said these were the most detailed discussions that the two sides had had , with `` a real back-and-forward between us , '' she also made clear that she was disappointed by the lack of progress made .

A senior U.S. administration official said Jalili directly engaged him in a 30 - to 40-minute question-and-answer exchange in the middle of Saturday 's plenary meeting .

`` The quality of the discussion was different because there was this back and forth , this Q and A , '' the official said . `` We just went back and forth with him . ''

Still , the official expressed disappointment , saying that Iran had `` put forward some minimal ideas and expected great return , and quite disproportionate return . ''

Britain , too , took a hard line after the talks .

`` The UK went to Kazakhstan ready with our partners to negotiate in good faith with Iran , '' British Foreign Secretary William Hague said in a statement . `` Iran 's current position falls far short of what is needed to achieve a diplomatic breakthrough . ''

When negotiators from the diplomatic bloc of six nations -- the United States , France , Britain , Germany , China and Russia -- last sat down with Iran 's envoy in Almaty in February , they delivered what they characterized as a `` fair and balanced offer '' to defuse tensions over the Iranian nuclear program .

Instead of delivering the `` concrete response '' Western governments had expected , Iran announced it was making its own proposal to the negotiating parties .

` Two-way street '

Jalili said Iran had tabled a proposal based on the discussions in Almaty and a previous meeting in Moscow -- and that it is now down to the six world powers to respond and show their `` willingness to take appropriate confidence-building steps in the future . ''

He repeated Tehran 's position that Iran has the right to a peaceful nuclear program .

`` Creating confidence is a two-way street , '' he said . Now , after many proposals put forward by Iran , it 's the turn of the six world powers to respond , he said .

Jalili 's comments on Iran 's enrichment of uranium -- one of the most contentious issues at stake -- reaffirmed Tehran 's right to pursue that track but also appeared to leave the door open to some kind of negotiation .

`` Enrichment is part of the rights of the Iranian people , whether we 're talking about 5 % or 20 % ... however , this can be an issue that can create further confidence , '' he said .

Jalili added that `` hostile behaviors '' directed toward Iran were detrimental to building confidence .

This was presumably a reference to the draconian sanctions imposed by Western governments against Tehran , which are crippling the Iranian economy . Oil exports have plummeted over the past several years , as has the value of Iran 's currency .

`` The purpose of any sanctions is to put pressure in order to get this process to work , '' said Ashton . `` And I believe we should continue to work as hard as we possibly can to make sure we are successful and we reach a satisfactory resolution . ''

Questions fly around any plan to attack Iran

The so-called P5 +1 governments are demanding that Iran come clean about its nuclear program , which they suspect includes covert development of nuclear weapons .

Iran consistently denies those charges , arguing it is enriching uranium and building nuclear reactors only for peaceful civilian energy needs .

Details of last February 's offer from the six countries represented across the negotiating table from Iran have not yet been made public .

Last month , technical experts from Iran and the P5 +1 countries met for more than 12 hours in Istanbul to discuss the proposal .

Iran 's deputy chief negotiator said the Iranian proposal tabled Friday was based on a previous PowerPoint presentation that the Iranian delegation submitted during a round of talks in Moscow in June 2012 .

`` The Islamic Republic of Iran proposed a practical method to implement the Moscow plan in a smaller scale , '' Ali Baghery said in a statement issued to journalists Friday . The offer , he said , was aimed at establishing `` a new bedrock of cooperation . ''

A call for ` concrete actions '

Washington has vowed it will continue to put pressure on Tehran .

`` As long as Iran does not take concrete steps to address the concerns of the international community about its nuclear program , the dual-track process continues . And that pressure only will increase if Iran does not begin to take concrete steps and concrete actions , '' said a senior U.S. administration official in a telephone briefing to journalists this week . The official spoke on condition of anonymity .

Iran argues that as a signatory to the Nuclear Non-Proliferation Treaty , development of nuclear technology is an inalienable right .

On the eve of the two-day talks in Kazakhstan , Jalili repeated this position in a speech given at a university in Almaty .

`` It is the right of the Iranian people to peaceful nuclear energy and most importantly to enrichment , '' Jalili said .

A report recently published by the Carnegie Endowment for International Peace concluded that sanctions are unlikely to force Tehran to give up its nuclear program .

The report , titled `` Iran 's Nuclear Odyssey , '' highlighted the fact that Tehran 's quest for a nuclear program has been going on for more than half a century , beginning under the rule of the pro-American shah , Reza Pahlavi , and continuing under the revolutionary Islamic republic that overthrew him .

`` The program 's cost -- measured in lost foreign investment and oil revenue -- has been well over $ 100 billion , '' Carnegie said .

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`` Iran 's current position falls far short of what is needed , '' says British official

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Iran has the right to enrich uranium , but negotiation may be possible , Saeed Jalili suggests

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It 's clear the two sides `` remain far apart '' on substance , EU foreign policy chief says

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No date or location is agreed upon for new talks between world powers and Iran